Currently, different techniques are used for detection of tumors and other evidence of cancer. For example, cancerous tumors in the lungs are usually located by using conventional x-rays. X-ray mammography, the modality commonly used for breast cancer screening, cannot distinguish between malignant and benign tumors, and is less effective for younger women with dense, fibrous breasts. Moreover, their high energy can ionize the tissue and may be potentially harmful if used too often for routine screening or at high intensity. If a tumor is suspected from an x-ray image, a biopsy that requires invasive removal of tissue from the suspect region needs to be performed to determine if the tumor is benign or malignant. In some cases, cytology rather than excisional biopsy is performed. However, both of these diagnostic procedures require physical removal of specimens followed by tissue processing in the laboratory. As such, these procedures incur a relatively high cost because specimen handling is required and, more importantly, diagnostic information is not available in real time. Moreover, in the context of detecting early neoplastic changes, both excisional biopsy and cytology can have unacceptable false negative rates, often arising from sampling errors. Another technique, radioisotope imaging, exposes the body to radioactivity that is potentially harmful. Ultrasound lacks the resolution to detect objects with linear dimensions smaller than a few millimeters, and like x-rays, do not provide any information about tissue chemistry. MRI is a powerful technique with sub-millimeter spatial resolution but the cost of superconducting magnets needed for its operation makes it very expensive.
From the standpoint of detecting early cancer and tumors, a primary technological challenge arises from the fact that laser light is highly scattered in all directions by tissue. The nascent but rapidly developing technology of optical tomography using a short pulse laser holds the promise of providing non-invasively detailed information about the tissue interior by measuring the temporal profile of the time-varying transmitted and reflected optical signals. In optical tomography, a short pulse laser is focused on the region to be probed and the time-dependent scattered fluence rates are measured at different locations using ultrafast detectors. It is the intent of the method to obtain information about the interior of the tissue medium non-invasively from the time-resolved fluence or intensity measurements. Optical tomography is expected to yield physiological information with a safer, simpler and less expensive system than the other types of methods.
The problem of determining the optical properties of tissues and tumors and hence the state of the tissues from experimentally measured time-dependant laser intensity measurements then requires the development of software using sophisticated inverse algorithm based on transient radiative transport formulation. Optical tomography will thus provide information about cancer and tumor properties, location, and size with high resolution, which is critical for tumor necrosis. To achieve these goals, detailed experimental study of delivery of laser energy with high efficiency in tissue samples, phantoms, biochemical species, and animals such as rats and mice have been performed. Delivery of pulsed laser light to the cancerous cells and tumor is done using hollow waveguides having different coatings for high transmission efficiency.
There is a need for an optical tomography system using a short-pulse laser for cancer diagnostics.